Obtaining carbon isotopic information for organic carbon from Martian sediments has long been a goal of planetary science, as it has the potential to elucidate the origin of such carbon and aspects ...of Martian carbon cycling. Carbon isotopic values (δ
C
) of the methane released during pyrolysis of 24 powder samples at Gale crater, Mars, show a high degree of variation (-137 ± 8‰ to +22 ± 10‰) when measured by the tunable laser spectrometer portion of the Sample Analysis at Mars instrument suite during evolved gas analysis. Included in these data are 10 measured δ
C values less than -70‰ found for six different sampling locations, all potentially associated with a possible paleosurface. There are multiple plausible explanations for the anomalously depleted
C observed in evolved methane, but no single explanation can be accepted without further research. Three possible explanations are the photolysis of biological methane released from the subsurface, photoreduction of atmospheric CO
, and deposition of cosmic dust during passage through a galactic molecular cloud. All three of these scenarios are unconventional, unlike processes common on Earth.
The Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) rover Curiosity detected evolved gases during thermal analysis of soil samples from the Rocknest aeolian deposit in ...Gale Crater. Major species detected (in order of decreasing molar abundance) were H2O, SO2, CO2, and O2, all at the µmol level, with HCl, H2S, NH3, NO, and HCN present at the tens to hundreds of nmol level. We compute weight % numbers for the major gases evolved by assuming a likely source and calculate abundances between 0.5 and 3 wt.%. The evolution of these gases implies the presence of both oxidized (perchlorates) and reduced (sulfides or H‐bearing) species as well as minerals formed under alkaline (carbonates) and possibly acidic (sulfates) conditions. Possible source phases in the Rocknest material are hydrated amorphous material, minor clay minerals, and hydrated perchlorate salts (all potential H2O sources), carbonates (CO2), perchlorates (O2 and HCl), and potential N‐bearing materials (e.g., Martian nitrates, terrestrial or Martian nitrogenated organics, ammonium salts) that evolve NH3, NO, and/or HCN. We conclude that Rocknest materials are a physical mixture in chemical disequilibrium, consistent with aeolian mixing, and that although weathering is not extensive, it may be ongoing even under current Martian surface conditions.
Key Points
Major volatiles detected by SAM were H2O, SO2, CO2, and O2
Minor volatiles include HCl, H2S, NH3, NO, and HCN
Calculating abundances from counts per second is explained
Recent attempts to resolve the faint young Sun paradox have focused on an early Earth atmosphere with elevated levels of the greenhouse gases methane (CH(4)) and carbon dioxide (CO(2)) that could ...have provided adequate warming to Earth's surface. On Titan, the photolysis of CH(4) has been shown to create a thick haze layer that cools its surface. Unlike Titan, however, early Earth's atmosphere likely contained high amounts of CO(2) and hydrogen (H(2)). In this work, we examine haze formation in an early Earth atmosphere composed of CO(2), H(2), N(2), and CH(4), with a CO(2)/CH(4) ratio of 10 and a H(2)/CO(2) ratio of up to 15. To initiate aerosol formation, a broad-spectrum ultraviolet (UV) energy source with emission at Lyman-alpha was used to simulate the solar spectrum. Aerosol composition and total aerosol mass produced as a function of reagent gas were measured with an aerosol mass spectrometer (AMS). Results show an order of magnitude decrease in haze production with the addition of H(2), with no significant change in the chemical composition of the haze. We calculate that the presence of H(2) on early Earth could thus have favored warmer surface temperatures and yet allowed photochemical haze formation to deliver complex organic species to early Earth's surface.
The aim of this study was to investigate musculoskeletal ultrasound (MSUS) as a diagnostic modality in DISH and to explore whether it might help in elucidating its pathogenesis and events that ...precede the calcification/ossification process. Fifty patients with DISH and 34 patients with osteoarthritis of the lower limbs without DISH were investigated. Data regarding demographics and traditional cardiovascular risk factors were collected from all patients. An ultrasonography was performed according to the Glasgow Ultrasound Enthesitis Scoring System (GUESS) by observers who were blinded to the diagnosis or the clinical findings in the patients. The total mean GUESS score for patients with DISH was 14.12 ± 5.2 and for patients without DISH 5.32 ± 4.99 (
P
< 0.0001). Univariate logistic regression analysis found a strong association between the GUESS and the probability of having DISH (
P
< 0.0001). The area under the ROC curve (AUC) revealed that the GUESS accuracy in diagnosing DISH was 88.53 % with sensitivity and specificity of 92 and 70.6 %, respectively, at a cutoff value of 6.36. A stepwise logistic regression analysis of the statistically significant items in the GUESS isolated four items, and the presence of either all of them or the first three items yielded the likelihood of having DISH to be 98.8 and 90.6 %, respectively. The GUESS and the stepwise logistic regression analysis of the GUESS items demonstrated a high likelihood of having DISH. MSUS might help to identify entheseal changes in DISH. Further studies are needed to confirm these results.
Videogaming platforms such as the Microsoft (Redmond, WA) Kinect(®) are increasingly being used in rehabilitation to improve balance performance and mobility. These gaming platforms do not have ...built-in clinical measures that offer clinically meaningful data. We have now developed software that will enable the Kinect sensor to assess a patient's balance using an interactive functional reach test (I-FRT). The aim of the study was to test the concurrent validity of the I-FRT and to establish the feasibility of implementing the I-FRT in a clinical setting.
The concurrent validity of the I-FRT was tested among 20 healthy adults (mean age, 25.8±3.4 years; 14 women). The Functional Reach Test (FRT) was measured simultaneously by both the Kinect sensor using the I-FRT software and the Optotrak Certus(®) 3D motion-capture system (Northern Digital Inc., Waterloo, ON, Canada). The feasibility of implementing the I-FRT in a clinical setting was assessed by performing the I-FRT in 10 participants with mild balance impairments recruited from the outpatient physical therapy clinic (mean age, 55.8±13.5 years; four women) and obtaining their feedback using a NASA Task Load Index (NASA-TLX) questionnaire.
There was moderate to good agreement between FRT measures made by the two measurement systems. The greatest agreement between the two measurement system was found with the Kinect sensor placed at a distance of 2.5 m intraclass correlation coefficient (2,k)=0.786; P<0.001 from the participant. Participants with mild balance impairments whose balance was assessed using the I-FRT software scored their experience favorably by assigning lower scores for the Frustration, Mental Demand, and Temporal Demand subscales on the NASA/TLX questionnaire.
FRT measures made using the Kinect sensor I-FRT software provides a valid clinical measure that can be used with the gaming platforms.
Apparent cyanobacterial emergence at about 2.8 Gya coincides with the negative excursion in the organic carbon isotope record, which is the first strong evidence for the presence of atmospheric ...methane. The existence of weathering feedbacks in the carbonate-silicate cycle suggests that atmospheric and oceanic CO2 concentrations would have been high prior to the presence of a methane greenhouse (and thus the ocean would have had high bicarbonate concentrations). With the onset of a methane greenhouse, carbon dioxide concentrations would decrease. Bicarbonate has been proposed as the preferred reductant that preceded water for oxygenic photosynthesis in a bacterial photosynthetic precursor to cyanobacteria; with the drop of carbon dioxide level, Archean cyanobacteria emerged using water as a reductant instead of bicarbonate (Dismukes et al., 2001). Our thermodynamic calculations, with regard to this scenario, give at least a tenfold drop in aqueous CO2 levels with the onset of a methane-dominated greenhouse, assuming surface temperatures of about 60 degrees C and a drop in the level of atmospheric carbon dioxide from about 1 to 0.1 bars. The buildup of atmospheric methane could have been triggered by the boost in oceanic organic productivity that arose from the emergence of pre-cyanobacterial oxygenic phototrophy at about 2.8-3.0 Gya; high temperatures may have precluded an earlier emergence. A greenhouse transition timescale on the order of 50-100 million years is consistent with results from modeling the carbonate-silicate cycle. This is an alternative hypothesis to proposals of a tectonic driver for this apparent greenhouse transition.
Recent studies have shown that clouds made of carbon dioxide ice may have warmed the surface of early Mars by reflecting not only incoming solar radiation but upwelling IR radiation as well. However, ...these studies have not treated scattering self-consistently in the thermal IR. Our own calculations, which treat IR scattering properly, confirm these earlier calculations but show that CO
2 clouds can also cool the surface, especially if they are low and optically thick. Estimating the actual effect of CO
2 clouds on early martian climate will require three-dimensional models in which cloud location, height, and optical depth, as well as surface temperature and pressure, are determined self-consistently. Our calculations further confirm that CO
2 clouds should extend the outer boundary of the habitable zone around a star but that there is still a finite limit beyond which above-freezing surface temperatures cannot be maintained by a CO
2–H
2O atmosphere. For our own Solar System, the absolute outer edge of the habitable zone is at ∼2.4 AU.
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